{"id":4234,"date":"2024-09-22T16:11:13","date_gmt":"2024-09-22T16:11:13","guid":{"rendered":"https:\/\/workhouse.sweetdishy.com\/?p=4234"},"modified":"2024-09-22T16:11:14","modified_gmt":"2024-09-22T16:11:14","slug":"the-doppler-effect","status":"publish","type":"post","link":"https:\/\/workhouse.sweetdishy.com\/index.php\/2024\/09\/22\/the-doppler-effect\/","title":{"rendered":"THE DOPPLER EFFECT"},"content":{"rendered":"\n

Lastly, if you built at least one of the units to act as both a transmitter and receiver, you essentially have the heart of a police radar gun, and you may want to experiment with the interesting wave property of light called the Doppler effect. Connect the Gunnplexer\u2019s detector diode output (mixer output) to an audio amplifier, such as the microphone input of an old cassette tape recorder.\u2021<\/sup><\/a> It is a good idea to place a 1-\u03bcF nonpolar capacitor between the Gunnplexer\u2019s output and the audio amplifier\u2019s input to get rid of any DC currents. Turn on the transmitter and point it at a passing car. The whooshing sound that you will hear is the Doppler shift caused on the reflected microwaves by the car\u2019s movement.<\/p>\n\n\n\n

Take a look at\u00a0Figure 19. The signal reflected by a stationary object illuminated by microwaves from the policeman\u2019s stationary radar gun is of the same frequency as the source. No \u201cbeat\u201d tone is generated when the transmitted and received frequencies are subtracted by the Gunnplexer\u2019s mixer diode. However, a moving object reflects a signal with frequency shifted in proportion to its speed relative to the stationary source. In this case, the mixer diode within the Gunnplexer reproduces the Doppler shift, and a microcomputer inside the radar gun can calculate the target\u2019s speed using the approximation:<\/p>\n\n\n\n

Figure 19\u00a0A Doppler radar illuminates its target with a microwave signal of frequency\u00a0t<\/sub><\/em>.\u00a0(a)<\/strong>\u00a0A stationary object simply reflects the signal at the same frequency. However, a moving target shifts the reflected signal by\u00a0f<\/em>Doppler<\/sub>\u00a0\u2248 2V ft<\/sub>\/c<\/em>, where\u00a0V<\/em>\u00a0is the relative velocity between the moving target and the radar gun, and\u00a0c<\/em>\u00a0is the speed of light.\"\"<\/p>\n\n\n\n

\"\"\/<\/figure>\n\n\n\n

where f<\/em>Doppler<\/sub> is the Doppler shift, V<\/em> is the relative velocity between the moving target and the radar gun, ft<\/sub><\/em> is the frequency of the illuminating microwave beam, and c<\/em> is the speed of light. When using a 10.5-GHz Gunnplexer, the Doppler shift for a car moving at 65 MPH (29.0576 m\/s) will be:<\/p>\n\n\n\n

\"\"\/<\/figure>\n\n\n\n

which is well within a human\u2019s hearing range. For each mile per hour of target speed, the Doppler shift will be equal to approximately 31.3 Hz.<\/p>\n\n\n\n

The reason for the shift in frequency is that, as the target approaches, each successive wave has to travel a shorter distance to reach the target before being reflected and detected. The returned waves are essentially compressed in the direction of travel, and the distance between wave crests decreases, thus decreasing the wavelength and increasing the frequency.<\/p>\n\n\n\n

If the radar is directed toward a target that is moving away, exactly the opposite situation occurs: each wave has to move farther, and the distance between wave crests increases, thus increasing the wavelength and decreasing the frequency. In either situation, the Gunnplexer generates the same beat tone for a certain velocity, whether the target is approaching or receding.<\/p>\n","protected":false},"excerpt":{"rendered":"

Lastly, if you built at least one of the units to act as both a transmitter and receiver, you essentially have the heart of a police radar gun, and you may want to experiment with the interesting wave property of light called the Doppler effect. Connect the Gunnplexer\u2019s detector diode output (mixer output) to an […]<\/p>\n","protected":false},"author":1,"featured_media":4166,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[511],"tags":[],"class_list":["post-4234","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-light-as-a-wave"],"jetpack_featured_media_url":"https:\/\/workhouse.sweetdishy.com\/wp-content\/uploads\/2024\/09\/lighthouse.png","_links":{"self":[{"href":"https:\/\/workhouse.sweetdishy.com\/index.php\/wp-json\/wp\/v2\/posts\/4234","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/workhouse.sweetdishy.com\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/workhouse.sweetdishy.com\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/workhouse.sweetdishy.com\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/workhouse.sweetdishy.com\/index.php\/wp-json\/wp\/v2\/comments?post=4234"}],"version-history":[{"count":1,"href":"https:\/\/workhouse.sweetdishy.com\/index.php\/wp-json\/wp\/v2\/posts\/4234\/revisions"}],"predecessor-version":[{"id":4239,"href":"https:\/\/workhouse.sweetdishy.com\/index.php\/wp-json\/wp\/v2\/posts\/4234\/revisions\/4239"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/workhouse.sweetdishy.com\/index.php\/wp-json\/wp\/v2\/media\/4166"}],"wp:attachment":[{"href":"https:\/\/workhouse.sweetdishy.com\/index.php\/wp-json\/wp\/v2\/media?parent=4234"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/workhouse.sweetdishy.com\/index.php\/wp-json\/wp\/v2\/categories?post=4234"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/workhouse.sweetdishy.com\/index.php\/wp-json\/wp\/v2\/tags?post=4234"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}